Roadway markers are utilized in a variety of traffic control applications. Many roadway markers are permanently affixed to a roadway to delineate lanes of traffic on a roadway. Other roadway markers are used to temporarily delineate lanes of traffic at construction or other work areas. Roadway markers used in such applications are called temporary roadway markers. Temporary roadway markers are usually attached to the surface of the roadway with a suitable adhesive that holds the marker in place during the temporary life of the roadway marker.
Temporary roadway markers serve to identify the edge of the road and lane lines, and notify motorists that caution is needed because a construction area is near. Temporary roadway markers often direct roadway traffic to pass along the portions of the roadway unaffected by the construction, while protecting workers within a construction area from roadway traffic. After the construction is complete, the temporary roadway markers are loosened and removed.
To be effective, temporary roadway markers must clearly alert oncoming traffic of the construction area. Typically, temporary roadway markers warn oncoming motorists by (1) the use of visual cues, such as brightly colored or reflective surfaces, or (2) the use of physical cues, such as causing a vehicle to rumble on contact with a roadway marker.
One example of a temporary roadway marker is described in U.S. Pat. No. 4,991,994, issued to Edouart. The Edouart patent describes a temporary roadway marker having a generally L-shaped configuration. One of the legs ("the base") of the L is designed to be attached to the roadway surface while the other leg extends upwardly from the roadway surface. The upstanding leg of the roadway marker has a reflective strip attached along its top edge. As with other prior temporary roadway markers, the reflective strip reflects the sun or a vehicle's headlights and improves the visual cue provided by the roadway marker. The upstanding leg raises the reflective strip above the surface of the road, thus helping to keep the reflective strip out of rubble, dust, or other materials present at construction sites. Keeping the reflective strip free of debris improves the ability of the temporary roadway marker to warn the motorist.
One of the notable failures of temporary roadway markers as described above is that they have a very short lifetime. When temporary roadway markers are used to mark the lane lines on a roadway construction project, they are often impacted by a vehicle's tire. This bends the upstanding leg of the roadway marker downwardly into contact with the road. If the roadway marker is not formed of a very flexible, resilient material, the bending can cause a permanent set and/or failure of the roadway marker in a very short number of cycles.
Prior art temporary roadway markers as described above are currently made of a single-hardness, flexible thermoplastic material, such as polyurethane. The flexibility of the polyurethane allows the leg of the roadway marker to bend over without breaking or cracking. A reflective strip is generally adhesively bonded to the top portion of the roadway marker. Although many different retro-reflective materials are available, very few have proven suitable for use on flexible roadway markers. Reflective strips made of materials such as flexible polyvinyl chloride, acrylic or polyester either provide insufficient reflectivity, are quick to delaminate upon impact with a vehicle tire, or otherwise degrade and are unsuitable for this use.
A proven retro-reflective material that provides sufficient retro-reflectivity and durability is polycarbonate. Polycarbonate reflective strips are made from thin sheet embossed with a cube-corner microprism pattern and then metalized to provide retro-reflectivity. Polycarbonate materials provide excellent optical performance and durability. Other high performance retro-reflective materials having similar optical performance and durability could also be used. The polycarbonates used to form the reflective strips have higher flexural modulis than the materials used to form the roadway marker.
Because the flexural modulus of the polycarbonate reflective strips and the body of the roadway marker differ, often by a factor of two or three, structural problems are produced when the upstanding leg of the roadway marker is bent or deformed. More specifically, as a vehicle contacts the roadway marker, the flexible body of the roadway marker flexes to a greater extent and at a greater rate than the stiffer reflective strip. The difference in the deformation of the reflective strip and body of the roadway marker creates stress concentrations at the interface between the reflective strip and body of the roadway marker. The stress concentrations cause the harder reflective strip to crack and eventually break up and become detached from the body of the roadway marker, reducing the visual cue provided by the roadway marker, particularly at night.
Some prior art roadway markers have attempted to remedy these problems by making the body of the roadway marker stiffer such that its flexural modulus is closer to that of the reflective strip. However, this decreases the life of the body of the roadway marker because stiffer materials are more susceptible to cracking and breaking during bending. Other prior art markers have attempted to remedy the problems by using a very flexible reflective material, such as 3M Engineer Grade sheeting. While not degrading quickly, the Engineer Grade sheeting has reflectivity of less than 10% that of polycarbonate, resulting in an unacceptably poor level of visibility at night.
Depending upon traffic volume, if the construction project on which the temporary roadway markers are used continues for more than a couple of weeks, the temporary roadway markers must be replaced, increasing expense. More specifically, the lifetime of a temporary roadway marker is directly related to how many impacts the roadway marker receives. The number of impacts is, of course, related to traffic volume. Under typical traffic conditions, temporary roadway markers last for approximately two weeks before they must be replaced.
In addition to the failure of temporary roadway markers due to loss of the reflective strip, temporary roadway markers are also prone to failure at the interface between the upstanding leg of the roadway marker and the base of the roadway marker. These failures result from the lack of elasticity in the sharp bend located at the interface. More specifically, most prior art temporary roadway markers consist of an L-shaped extrusion. The L-shaped extrusion includes curved fillet located where the base leg and the upstanding leg of the roadway marker are joined. The fillet increases the amount of material at the interface between the base and leg of the roadway marker. The additional material increases the stiffness of the roadway marker at the interface. The increased stiffness, in turn, produces local stress concentrations at the interface between the base and leg when the leg is bent due to contact with a vehicle's tire. The local stress concentrations lead to failure of the roadway marker after an undesirably small number of cycles.
In addition to the stress concentrations caused by the increased material at the interface, some prior art roadway markers allow the upstanding leg to be bent such that a very small radius of curvature is produced at the interface between the leg and the base of the roadway marker. The tight radius of curvature produces very large stress concentrations which further contribute to failure of the roadway marker.
The present invention is directed to providing a temporary roadway marker that overcomes the foregoing disadvantages of prior and temporary roadway markers.